The terms horns and antlers are often used interchangeably, but in reality, they refer to quite different structures. Antlers are a pair of bony, branched structures that protrude from the frontals of the skull of animals and are shed annually; horns are also paired and protrude from the frontal, but they are permanent, unbranched, and made up of a bony core and a keratinized sheath.

Antlers are one of the most easily recognized characteristics of the family Cervidae. They are present only in males (with the exception of caribou) and are capable of growing astoundingly large.Caribou and reindeer use their antlers to clear away snow so they can eat the vegetation underneath. This is one possible reason that females of this species evolved antlers. Another possible reason is for female competition during winter foraging.

Males use their full-grown antlers during the breeding season in social interactions in competition for females. In winter, pituitary antler-growth hormone stimulation decreases as day length shortens, and androgen secretion lessens. As a result, the pedicel loses calcium, weakening the point of connection between it and the antler, and eventually the antlers are shed. Males then are without antlers for a few months in late winter until the cycle begins again. Curiously, some cervids have large canine teeth, which are used in sexual displays and fighting. Often species with large canines have small antlers or are missing antlers altogether.

As antlers near the end of the growing process, spongy bone in their outer edges is replaced by compact bone, while their centers become filled with coarse, spongy, lamellar bone and marrow spaces. The velvet dies and is removed in part by the animals rubbing and thrashing their antlers against vegetation. The antlers also are stained during this action, giving them the brown, polished, wooden look.

HORNS:

Horns occur in males of all species of Bovidae, and females often bear them too. Horns are composed of a bony core covered with a sheath of keratin. Unlike antlers, horns are never branched, but they do vary from species to species in shape and size.